Characters and stories is everything. It keeps consumers invested and loyal to the franchise, even when the gameplay is boring and repetative, instead of jumping ship to a game with equal mechanics. It's why so many still cosplay as Kerrigan, Mario, Link, etc.
It's how so many people remember Ezio and Altair instead of the other forgettable characters that followed.
I see fromsoft cosplay and the main character with no lines as well. It may be as factor but it's far from "everything". Bioshock infinite was a crappy game with a good cosplay character who most who cosplay as her have no idea what bioshock infinite is.
Meanwhile the non-campaign gameplay, while polished, is hardly innovative (a common issue with the commercial RTS games compared to the fan-made ones).